erc-c/include/apple2.h

#ifndef _APPLE2_H_
#define _APPLE2_H_

#include "apple2.dd.h"
#include "mos6502.h"
#include "vm_bitfont.h"
#include "vm_screen.h"

/*
 * This is the size of the bitmap font we use for the apple2
 */
#define APPLE2_SYSFONT_SIZE 21558

/*
 * The reset vector is the address where the apple will consult to
 * figure out where control should go after a reset. Think of this as
 * something like a pointer to a main() function in C. That is: where's
 * the main function? Let's ask the reset vector!
 */
#define APPLE2_RESET_VECTOR 0x03F2

/*
 * This is the address of the validity-check byte, aka the power-up
 * byte. The Apple II will use this to see if the reset vector is valid.
 */
#define APPLE2_POWERUP_BYTE 0x03F4

/*
 * I'm not _exactly_ clear on where the applesoft interpreter lives in
 * ROM, after spending possibly too-much time researching how this
 * works. My guess is I'm missing something that's obvious to others.
 * $E000 seems to be the original spot that Integer BASIC was contained,
 * and I'm going to guess Applesoft BASIC is in the same spot. Here's
 * hoping!
 */
#define APPLE2_APPLESOFT_MAIN 0xE000

enum video_modes {
    VIDEO_40COL_TEXT,
    VIDEO_LORES,
    VIDEO_HIRES,
    VIDEO_80COL_TEXT,
    VIDEO_DOUBLE_LORES,
    VIDEO_DOUBLE_HIRES,
};

enum color_modes {
    COLOR_GREEN,
    COLOR_AMBER,
    COLOR_GRAY,
    COLOR_FULL,
};

enum lores_colors {
    LORES_BLACK,
    LORES_MAGENTA,
    LORES_DARKBLUE,
    LORES_PURPLE,
    LORES_DARKGREEN,
    LORES_GRAY1,
    LORES_MEDBLUE,
    LORES_LIGHTBLUE,
    LORES_BROWN,
    LORES_ORANGE,
    LORES_GRAY2,
    LORES_PINK,
    LORES_LIGHTGREEN,
    LORES_YELLOW,
    LORES_AQUAMARINE,
    LORES_WHITE,
};

// Write-protect on/off.
// Read target = ROM or RAM.
// Write target = RAM.
// Set mode of $Dxxx hexapage bank1 or bank2 ram.

// 0 - 0=off 1=on
// 1 - 0=ROM 1=RAM
// 2 - 0=BANK1 1=BANK2

/*
 * An Apple II has bank-switched memory beginning with $D000 extending
 * through $FFFF. The enums below define bit flag names to determine
 * what is accessible through those addresses.
 *
 * Note that it _is_ possible to write while reading ROM, but your
 * writes will not go to ROM; they'll go to _RAM_. Any write to $E000 -
 * $FFFF may only be sent to bank 1 RAM. Writes to $D000-$DFFF may
 * either be sent to bank 1 RAM or bank 2 RAM based upon the RAM2 bit
 * flag below.
 */
enum memory_mode {
    MEMORY_ROM = 1,         // on = read ROM; off = read RAM
    MEMORY_WRITE = 2,       // on = allow writes to RAM; off = disallow writes
    MEMORY_RAM2 = 4,        // on = use bank 2 for $D000-$DFFF; off = use bank 1
};

typedef struct {
    /*
     * The apple 2 hardware used an MOS-6502 processor.
     */
    mos6502 *cpu;

    /*
     * This is the literal memory that the CPU above will create. You
     * should _not_ attempt to free this memory; allow the CPU's own
     * delete function to do that.
     */
    vm_segment *memory;

    /*
     * The Apple II used a system of bank-switched memory to enable
     * software to address a separate block of ROM.
     */
    vm_segment *rom;
    
    /*
     * Additionally, the Apple II had a standalone block of RAM (with no
     * good name for it, really, hence the regrettably vague "ram2") so
     * that you technically could use 16k of RAM from a set of 12k
     * addresses. The extra 4k lives a lonely life in the garage
     * apartment.
     */
    vm_segment *ram2;

    /*
     * The Apple II may have an auxiliary RAM bank; this was possible by
     * installing a card there. If you had the 80-column text card (and
     * you likely did), then you got an extra kilobyte of RAM to work
     * with; it was either used for the extra columns or you could take
     * advantage of it for extra storage otherwise.
     */
    vm_segment *aux;

    /*
     * The screen wherein we shall render all of our graphics.
     */
    vm_screen *screen;

    /*
     * This is the system font (the only font the Apple II knows about,
     * really); anywhere we render text, we have to use this font.
     */
    vm_bitfont *sysfont;

    /*
     * This is the mode in which we must interpret graphics. This will
     * tell us not only if we're in lo- or hi-res, but also if we are in
     * single or double view mode.
     */
    int video_mode;

    /*
     * This is the color mode we want to emulate. You can have a few
     * different styles of monochromatic displays: green, amber, and
     * light gray on black; you can also emulate a full color display,
     * in which text mode tends to look like light gray.
     */
    int color_mode;

    /*
     * This describes the behavior of our bank-switching scheme. We need
     * our read/write mappers to know where writes into the
     * bank-switched area of memory should target.
     */
    vm_8bit bank_switch;

    /*
     * Our two disk drives.
     */
    apple2dd *drive1;
    apple2dd *drive2;
} apple2;

extern apple2 *apple2_create(int, int);
extern bool apple2_is_double_video(apple2 *);
extern int apple2_boot(apple2 *);
extern void apple2_clear_strobe(apple2 *);
extern void apple2_free(apple2 *);
extern void apple2_press_key(apple2 *, vm_8bit);
extern void apple2_release_key(apple2 *);
extern void apple2_reset(apple2 *);
extern void apple2_run_loop(apple2 *);
extern void apple2_set_color(apple2 *, int);
extern void apple2_set_bank_switch(apple2 *, vm_8bit);
extern void apple2_set_video(apple2 *, int);

#endif